tests/__init__.py keeps a run offline, its scratch under tmp/ and its
installer cache its own, but only discover -s tests -t . imported it.
discover tests ran with RETROBIOS_OFFLINE unset, scratch on the /tmp
tmpfs and the user's real installer cache, the setting in which e2e
fixtures had written into the shared .cache/large. Every test module now
imports the package first, and a test fails on a module that does not.
test_verify_listing.py took its line with the previous commit.
Run ruff check --fix: remove unused imports (F401), fix f-strings
without placeholders (F541), remove unused variables (F841), fix
duplicate dict key (F601).
Run isort --profile black: normalize import ordering across all files.
Run ruff format: apply consistent formatting (black-compatible) to
all 58 Python files.
3 intentional E402 remain (imports after require_yaml() must execute
after yaml is available).
Abdessamad Derraz